During the detailed 20-week scan, we look carefully at your baby for features that can sometimes be linked with a chromosomal or genetic condition. Being told that your baby has a "marker" can be worrying, but most markers turn out to be harmless, particularly if you have already had reassuring screening earlier in pregnancy.
This guide explains what genetic markers and soft markers are, why they are less concerning than they used to be, and when further tests may be helpful.
Key points
- Genetic markers and soft markers are ultrasound findings that can be linked with chromosomal or genetic conditions.
- Finding a marker does not mean that your baby has a genetic condition.
- Many soft markers are minor variations commonly seen in healthy babies.
- After a low-risk NIPT or combined screening result, a single soft marker is usually much less concerning.
- Some findings still need further assessment, for reasons that may have nothing to do with Down's syndrome.
- What matters most is the whole scan, considered together with your previous screening results.
What are genetic markers and soft markers?
Some features or measurements seen on ultrasound can be linked with chromosomal conditions such as Down's syndrome (trisomy 21), Edwards' syndrome (trisomy 18) and Patau's syndrome (trisomy 13), or with other genetic conditions. These are called genetic markers or soft markers.
At The Pregnancy Clinic, we look for these markers as part of our detailed consultant-led scan at 20–22 weeks. The findings fall into three groups:
- Normal: no markers are seen.
- Genetic markers: features, or combinations of features, that may point to an underlying chromosomal or genetic condition.
- Soft markers: minor findings that have been linked with chromosomal conditions, particularly Down's syndrome, but are often seen in healthy babies.
The significance of a marker depends on what it is, whether there are other findings, and the results of any screening you had earlier in pregnancy.
What are genetic markers?
Genetic markers are features of your baby's anatomy that may be linked with a chromosomal or genetic condition. Some are subtle and others more obvious. A single marker does not necessarily mean there is a problem, but several markers together may raise more concern.
| Genetic marker | What it means |
|---|---|
| Frontal bossing | An unusually prominent forehead |
| Facial cleft | A cleft of the upper lip or palate |
| Micrognathia | An unusually small or receding chin |
| Prenasal oedema | Extra soft tissue or swelling over the bridge of the nose |
| Abnormal head shape | An unusually rounded, elongated or cloverleaf-shaped skull |
| Ventriculomegaly | Extra fluid in the fluid spaces (ventricles) of the brain |
| Increased nuchal fold | Thicker soft tissue at the back of the baby's neck |
| Aberrant right subclavian artery (ARSA) | An artery near the heart that follows an unusual path |
| Ventricular septal defect (VSD) | A small hole between the two lower chambers of the heart |
| Small or absent stomach | The stomach looks small or cannot be seen |
| Hydronephrosis | Widening of the part of the kidney that collects urine |
| Echogenic bowel | The baby's bowel looks unusually bright on the scan |
| Exomphalos | Some of the abdominal organs sit in a sac outside the tummy, where the cord joins |
| Short femur or humerus | The thigh or upper-arm bone is shorter than expected |
| Abnormal amniotic fluid | Too much or too little fluid around the baby |
These findings vary a great deal in importance. A slightly short thigh bone may simply be normal variation, whereas an unusual head shape, or several unusual facial features together, may raise more concern. Likewise, mild widening of the kidneys is common, while more significant kidney abnormalities need detailed assessment.
What matters is not just whether a marker is present, but how it looks, how marked it is, and whether there are other findings.
What are soft markers?
Soft markers are minor ultrasound findings that have been linked with a higher chance of Down's syndrome. They are common at the 20-week scan and are often seen in babies with completely normal chromosomes. On their own, soft markers do not usually affect your baby's health or development.
Why are soft markers less worrying than they used to be?
In the past, screening for Down's syndrome was less accurate, so some affected pregnancies were only picked up at the 20-week scan. Soft markers were therefore an important extra clue.
Today, most women have much more accurate screening earlier in pregnancy:
| Screening test | When | Approximate detection of Down's syndrome |
|---|---|---|
| Quadruple blood test (older approach) | Second trimester | 65% |
| Combined screening | 11–14 weeks | 85% |
| NIPT | From 10 weeks | Over 99% |
This means that:
- Most babies with Down's syndrome are now identified before the 20-week scan.
- A single soft marker after a low-risk NIPT result is usually not a concern, because the NIPT result has already made Down's syndrome very unlikely.
- Several markers together still need careful assessment, as NIPT does not rule out every chromosomal or genetic condition.
- Some markers matter for other reasons. For example, extra fluid in the brain may be linked with brain development or infection, widened kidneys may need a follow-up scan, and short long bones may need a check of your baby's growth.
How much does a single soft marker change the chance of Down's syndrome?
A large review of 48 studies, published in 2013, looked at how much each soft marker changes the chance of Down's syndrome when it is found on its own and the rest of the scan is normal. The result is given as a likelihood ratio:
- About 1: the chance is essentially unchanged.
- More than 1: the chance goes up (for example, 4 means about four times higher than before).
- Less than 1: the chance goes down.
| Soft marker found on its own | Likelihood ratio | What this means |
|---|---|---|
| Echogenic intracardiac focus (bright spot in the heart) | 0.95 | No real change |
| Mild hydronephrosis (mildly widened kidneys) | 1.08 | No real change |
| Short femur (thigh bone) | 0.61 | Chance slightly lower |
| Short humerus (upper-arm bone) | 0.78 | Chance slightly lower |
| Echogenic bowel | 1.65 | Small increase |
| Mild ventriculomegaly | 3.81 | About four times higher |
| Aberrant right subclavian artery (ARSA) | 3.94 | About four times higher |
| Increased nuchal fold | 3.79 | About four times higher |
| Absent or small nasal bone | 6.58 | About six to seven times higher |
Source: Agathokleous M, et al. Ultrasound Obstet Gynecol. 2013;41:247–261.
Even a four-fold increase can still leave the chance low. For example, if your NIPT result was low risk, a fourfold increase usually still means a very small chance. These figures also come mostly from studies carried out before NIPT was widely used, so we interpret them with care.
What if only one soft marker is found?
If the rest of the scan is normal, this is called an isolated soft marker. Its significance depends on which marker it is and your earlier screening results. For example:
- A bright spot in the heart after a low-risk NIPT is usually of no significance.
- A slightly short thigh or arm bone after a low-risk NIPT is unlikely to mean Down's syndrome, although we may check your baby's growth later.
- Mildly widened kidneys may need a follow-up scan.
- Extra fluid in the brain (ventriculomegaly) needs more detailed assessment, as it can have other causes.
So not every isolated marker needs the same tests or follow-up.
What if several markers are found?
When more than one marker is present, the chance of an underlying chromosomal condition may be higher, especially if you have not had screening earlier in pregnancy. However, it is not simply a matter of counting markers. The type of marker, how marked it is, any other findings and your earlier screening results all matter. A detailed fetal medicine assessment helps decide whether further tests are needed.
What if I have already had a low-risk NIPT?
A low-risk NIPT result is very reassuring for Down's syndrome and the other common trisomies it tests for. If a single minor soft marker is then found, the chance of Down's syndrome usually remains very low, and for findings such as a bright spot in the heart, no further genetic tests are usually needed.
However, NIPT does not rule out every chromosomal or genetic condition, and some findings, such as ventriculomegaly, may need further tests whatever the NIPT result.
What if I have not had any screening?
If you have not had screening, finding a soft marker is a good opportunity to discuss your options. If there is a single minor marker and nothing else of concern, NIPT may be a suitable next step. If there are more significant markers or several findings, a diagnostic test such as amniocentesis may be more appropriate. We will help you decide what is right for you.
What happens if a genetic marker is found?
We carefully examine the rest of your baby's anatomy to see whether the finding is on its own or part of a wider pattern, and we take your earlier screening results (combined screening or NIPT) into account. Depending on the findings, we may discuss the option of further genetic testing, such as an amniocentesis. Not every marker needs genetic testing, and many isolated findings have a good outcome.
We will also share the findings with your local NHS Fetal Medicine Unit for further management and ongoing care.
How does The Pregnancy Clinic assess genetic and soft markers?
Assessment of genetic and soft markers is an important part of our detailed consultant-led scan at 20–22 weeks. Our approach includes:
- Detailed ultrasound assessment of your baby's anatomy to identify any markers.
- Assessment of each marker: how it looks, how marked it is and what it may mean.
- Review of your earlier screening: combined screening, NIPT or any previous test results.
- Checking for other findings, to see whether a marker is isolated.
- Personalised counselling about what the findings mean and whether further tests would help.
- Further tests when needed, such as diagnostic genetic testing or additional specialist scans.
Our aim is to give you accurate information, while avoiding unnecessary worry or tests when a finding is likely to be a normal variation.
Related pregnancy guides
Frequently asked questions
Does a soft marker mean my baby has Down's syndrome?
No. Soft markers are common and are often seen in healthy babies. Many, such as a bright spot in the heart, make little or no difference to the chance of Down's syndrome when found on their own.
I had a low-risk NIPT. Should I worry about a soft marker?
Usually not. After a low-risk NIPT, a single minor soft marker is unlikely to mean Down's syndrome. Some findings, such as extra fluid in the brain, may still need further assessment for other reasons.
What is the difference between a genetic marker and a soft marker?
Genetic markers are features that may point to a chromosomal or genetic condition. Soft markers are minor findings that have been linked with Down's syndrome but are frequently seen in babies with normal chromosomes.
Will I need an amniocentesis?
Not usually for a single minor soft marker. An amniocentesis may be discussed if there are significant markers, several findings together, or other abnormalities on the scan.
What does a likelihood ratio mean?
It shows how much a finding changes the chance of a condition. A value of about 1 means no real change, above 1 means the chance goes up and below 1 means it goes down.
Book your detailed 20-week scan at The Pregnancy Clinic
At The Pregnancy Clinic, our consultant-led 20–22-week examinations include a detailed assessment of your baby's anatomy and of ultrasound markers linked with chromosomal and genetic conditions.
We interpret any findings alongside your previous screening results and give you personalised advice about what they mean and whether further tests would help.
Book your detailed 20-week scan →This article provides general educational information and does not replace personalised medical advice. The Pregnancy Clinic provides planned appointments only; for urgent concerns, please contact your maternity unit, NHS 111 or your GP.
Clinical references
- Agathokleous M, Chaveeva P, Poon LCY, Kosinski P, Nicolaides KH. Meta-analysis of second-trimester markers for trisomy 21. Ultrasound Obstet Gynecol. 2013;41(3):247–261.
- Society for Maternal-Fetal Medicine. Consult Series #57: Evaluation and management of isolated soft ultrasound markers for aneuploidy in the second trimester. Am J Obstet Gynecol. 2021;225(4):B2–B15.
- Salomon LJ, et al. ISUOG Practice Guidelines (updated): performance of the routine mid-trimester fetal ultrasound scan. Ultrasound Obstet Gynecol. 2022;59:840–856.
- NHS. Screening for Down's syndrome, Edwards' syndrome and Patau's syndrome.
- National Institute for Health and Care Excellence (NICE). Antenatal care. NICE guideline NG201.